Immunogenicity and protective efficacy of an inactivated α-toxin toxoid vaccine candidate against Clostridium perfringens type A in sika deer

Clostridium perfringens type A is associated with acute hemorrhagic enteritis and enterotoxemia in sika deer, but no species-specific vaccine is currently available. In this preliminary target-animal proof-of-concept study, a formalin-inactivated recombinant α-toxin toxoid vaccine candidate was prepared and evaluated in ten 6-month-old female sika deer, with five animals assigned to the Immunized group and five to the adjuvant-Control group. Deer were immunized on days 0 and 14 and challenged on day 28 using a controlled homologous intraperitoneal LD 100 bacterial challenge model. Immunization induced higher antigen-specific antibody responses than the control treatment, as shown by ELISA AUC analysis based on individual deer sera (1.008 ± 0.140 vs. 0.430 ± 0.027; mean difference, 0.578; 95% CI, 0.406–0.750; Welch’s t-test, P < 0.001). Immune sera neutralized the hemolytic and phospholipase activities of α-toxin, and the mouse neutralization assay indicated a reciprocal serum neutralizing antibody titer of 128, corresponding to the highest protective serum dilution of 2⁻⁷. After the challenge, all immunized deer survived without obvious clinical signs, whereas all control deer died within 6 h. Serum α-toxin concentrations were also lower in immunized deer than in controls (31.16 ± 4.28 vs. 88.60 ± 7.90 ng/mL; P < 0.0001), and total histopathological lesion scores were reduced [3 (3–4) vs. 18 (17–18)]. These findings indicate that the α-toxin toxoid candidate induced toxin-neutralizing humoral immunity and protected sika deer under a controlled intraperitoneal lethal challenge model. However, because this was a small exploratory study and the challenge route bypassed natural gastrointestinal infection, larger target-animal studies, oral or intestinal challenge models, dose optimization, immune-duration assessment, and field trials are required before practical application can be inferred.